1. Field of the Invention
The present invention relates generally to methods and apparatus for plasma enhanced chemical vapor deposition (PECVD) on wafers and plasma enhanced etching of wafers, and more particularly to a method and apparatus for transmitting RF energy to create a localized glow discharge over surfaces of wafers stacked vertically on a rotating wafer boat, and apparatus for robotically inserting and removing the wafers.
2. Brief Description of the Prior Art
There are a large number of plasma enhanced processes that are performed inside of enclosed chambers wherein the pressure, temperature, composition of gases and application of radio frequency (RF) power are controlled to (a) produce the desired thin film deposition of various materials onto substrates such as semiconductor wafers, flat panel displays and others, and (b) to remove various materials from such substrates via etching. For convenience, the term "wafer" as used in the following description of the prior art and in the disclosure of the present invention will be used with the understanding that the invention also applies to the manufacture of flat panel displays and other types of substrates or devices wherein plasma enhanced processes are employed. For example, silicon nitride is typically deposited via plasma enhanced chemical vapor deposition (PECVD) on top of metal layers on a semiconductor wafer. A main feature of PECVD processes is that they can be carried out at low substrate temperatures as described by S. Wolf and R. N. Tauber, "Silicon Processing for the VLSI Era", Volume 1-Process Technology, Lattice Press, 1986, pp. 171-174. FIG. 1 shows a chamber 10 having a rotating susceptor 12 capable of holding a plurality of substrates. RF energy is applied to an upper electrode 14 to create an electric field causing a plasma (glow discharge) creating free electrons within the plasma region 16. The electrons gain sufficient energy from the electric field so that when they collide with gas molecules, gas-phase dissociation and ionization of the reactant gases (e.g. silane and nitrogen) occurs. The energetic species are then adsorbed on the film surface.
FIG. 2 shows another prior art device including a single wafer PECVD chamber 18 wherein a wafer 20 is held stationary. There are a variety of single wafer PECVD chamber designs available in the marketplace. There are also a variety of commercially available multiple wafer chambers as described above wherein the wafers are all supported by a susceptor in a single horizontal plane.
The single wafer and horizontal multiple wafer PECVD chamber designs discussed above are problematic for numerous reasons. First, such single wafer designs suffer from relatively low throughput as only one wafer at a time can be processed. Further, the multiple wafer horizontal designs pose extreme difficulties in connection with the incorporation of automatic robotic wafer loading and unloading. Also, horizontal multiple wafer designs can process only a limited number of wafers before the chamber becomes so large in area as to become very difficult to maintain the necessary plasma uniformity and necessary gas flow control.